Creating a Spinach & Mushroom Frittata is straightforward if you follow these simple steps:

1. Preheat Oven: Preheat your oven to 375°F (190°C).
2. Sauté Vegetables: In an oven-safe skillet, heat olive oil over medium heat. Add diced onions and bell peppers, cooking until softened (about 3-4 minutes).
3. Add Mushrooms: Stir in the sliced mushrooms and cook for an additional 3-4 minutes until they are tender and browned.
4. Incorporate Spinach: Add the chopped spinach to the skillet, stirring until wilted (about 1-2 minutes). Season with salt and pepper.
5. Whisk Eggs: In a bowl, whisk the eggs until well combined. Pour the eggs evenly over the sautéed vegetables in the skillet.
6. Add Cheese: Sprinkle the shredded cheese on top of the egg mixture.
7. Cook on Stovetop: Cook on the stovetop for about 3-4 minutes, allowing the edges to set slightly.
8. Transfer to Oven: Carefully transfer the skillet to the preheated oven. Bake for 15-20 minutes, or until the eggs are fully set and the top is lightly golden.
9. Cool and Slice: Remove from the oven and let cool for a few minutes before slicing.
10. Serve: Garnish with fresh herbs if desired, and serve warm.

These steps will guide you through creating a delectable Spinach & Mushroom Frittata that is sure to impress your family and friends.